In recent years, many communication infrastructures have adopted a network configuration in which networks are connected to each other using a gateway.
Further, many communication infrastructures operate a plurality of gateway apparatus in a redundancy configuration.
To configure redundancy of a plurality of gateway apparatus, there is often adopted an architecture (active-standby configuration) of one gateway apparatus being set to an active system and another gateway apparatus being set to a standby system, to cause standby system resources to stand by in a standby mode.
Meanwhile, there is also known an architecture (active-active configuration) of two gateway apparatus being associated with each other to form a dependency relationship between an active system and a standby system and to operate both the gateway apparatus as active systems. In this architecture, when one of two gateway apparatus in a redundancy configuration has failed, the other gateway apparatus switches to the active system for handling a subscriber terminal of the failed gateway apparatus. Thus, redundancy of communication by subscribers is secured. The active-active configuration is superior to the active-standby configuration in terms of load balancing characteristics.
Related art is disclosed in Patent Document 1 and Patent Document 2. Further, technologies of components to be used in a network system are disclosed in, for example, Non Patent Document 1 and Non Patent Document 2.
In Patent Document 1, there is disclosed a packet transfer system for relaying packets between subscriber terminals and the Internet. The packet transfer system is configured to connect an access network to a relay network using a gateway apparatus as its architecture for relaying packets to be communicated between an arbitrary subscriber terminal and the Internet. Further, in this network architecture, two gateway apparatus that connect the access network to the relay network in a redundancy configuration handle the subscriber terminals.
In Patent Document 2, there is disclosed a system having a network architecture similar to that of Patent Document 1, which includes a gateway load balancing apparatus in an access network as a system for balancing loads of a group of subscriber terminals among a plurality of gateway apparatus.
In Non Patent Document 1, there is disclosed a request for comments (RFC) specifying the virtual router redundancy protocol (VRRP), which is described as an example of a redundancy protocol in an embodiment of this invention.
In Non Patent Document 2, there is disclosed an RFC specifying IPv6 router advertisement (RA), which is described as an example of IP prefix advertisement in an embodiment of this invention.